Measurement of CP violation at a Neutrino Factory

The prospects of measuring CP violation in the leptonic sector using the intense neutrino beams arising from muon decay in the straight sections of a muon accumulator ring (the so-called neutrino factory) are discussed.Comment: Invited talk given at the CP2000 Conference in Ferrara, September, 200

CP Trajectory Diagram; A tool for pictorial representation of CP and matter effects in neutrino oscillations

We introduce "CP trajectory diagram in bi-probability space" as a powerful tool for pictorial representation of the genuine CP and the matter effects in neutrino oscillations. Existence of the correlated ambiguity in a determination of CP violating phase \delta and the sign of \Delta m^2_{13} is uncovered. Principles of tuning beam energy for a given baseline distance are proposed to resolve the ambiguity and to maximize the CP-odd effect. We finally point out, quite contrary to what is usually believed, that the ambiguity may be resolved with 50 % chance in the super-JHF experiment despite its relatively short baseline of 300 km.Comment: 6 pages with 2 postscript figures. Talk presented at The 3rd International Workshop on Neutrino Factories Based on Muon Storage Rings (NuFACT01), Tsukuba, Japan, May 24-30, 200

Natural Mass Generation for the Sterile Neutrino

We point out that there is a serious cosmological problem in the supersymmetric standard model if a sterile neutrino is responsible for the solar neutrino oscillation, and propose a possible solution to this problem. We show that our solution induces naturally a mass of order 10^{-4} eV for the sterile neutrino, which is deeply related to the mechanism of supersymmetry breaking.Comment: 8 pages, no figures, minor changes, reference adde

The Three Neutrino Scenario

I have discussed in my talk several remaining issues in the standard three-flavor mixing scheme of neutrinos, in particilar, the sign of $\Delta m^2_{13}$ and the leptonic CP violating phase. In this report I focus on two topics: (1) supernova method for determining the former sign, and (2) illuminating how one can detect the signatures for both of them in long-baseline (\gsim 10 km) neutrino oscillation experiments. I do this by formulating perturbative frameworks appropriate for the two typical options of such experiments, the high energy and the low energy options with beam energies of $\sim$ 10 GeV and $\sim$ 100 MeV, respectively.Comment: 6 pages, Latex, 2 figures. Talk presented at Europhysics Neutrino Oscillation Workshop (NOW2000), Otranto, Italy, September 9-16, 200

Stability of Neutral Fermi Balls with Multi-Flavor Fermions

A Fermi ball is a kind of non-topological soliton, which is thought to arise from the spontaneous breaking of an approximate $Z_2$ symmetry and to contribute to cold dark matter. We consider a simple model in which fermion fields with multi-flavors are coupled to a scalar field through Yukawa coupling, and examine how the number of the fermion flavors affects the stability of the Fermi ball against the fragmentation. (1)We find that the Fermi ball is stable against the fragmentation in most cases even in the lowest order thin-wall approximation. (2)We then find that in the other specific cases, the stability is marginal in the lowest order thin-wall approximation, and the next-to-leading order correction determines the stable region of the coupling constants; We examine the simplest case where the total fermion number $N_i$ and the Yukawa coupling constant $G_i$ of each flavor $i$ are common to the flavor, and find that the Fermi ball is stable in the limited region of the parameters and has the broader region for the larger number of the flavors.Comment: 10 pages, 3 eps figures, ReVTeX

The Two Loop Long Range Effect on the Proton Decay Effective Lagrangian

We calculate the two loop long range effect on the proton decay effective Lagrangian. Numerical calculation for suppression factor gives $A_L($2-loop$) = 0.321$ for the value of the strong coupling constant $\alpha_s(m_Z) = 0.116$. Two loop effect to more general effective Lagrangian is also given.Comment: 11 pages, 1 figures(uuencoded postscript file

Proposal of a Simple Method to Estimate Neutrino Oscillation Probability and CP Violation in Matter

We study neutrino oscillation within the framework of three generations in matter. We propose a simple method to approximate the coefficients A, B and C which do not depend on the CP phase \delta in the oscillation probability P(\nu_e \to \nu_{\mu})=A\cos \delta + B\sin \delta +C. An advantage of our method is that an approximate formula of the coefficients A, B and C in arbitrary matter {\it without the usual first order perturbative calculations} of the small parameter \Delta m_{21}^2/\Delta m_{31}^2 or \sin \theta_{13} can be derived. Furthermore we show that all the approximate formulas for low, intermediate and high energy regions given by other authors in constant matter can be easily derived from our formula. It means that our formula is applicable over a wide energy region.Comment: 15 pages, 9 figures, accepted version in PL

Method for Determination of ∣Ue3∣|U_{e3}| in Neutrino Oscillation Appearance Experiments

We point out that determination of the MNS matrix element |U_{e3}| = s_{13} in long-baseline \nu_{\mu} \to \nu_e neutrino oscillation experiments suffers from large intrinsic uncertainty due to the unknown CP violating phase \delta and sign of \Delta m^2_{13}. We propose a new strategy for accurate determination of $\theta_{13}$; tune the beam energy at the oscillation maximum and do the measurement both in neutrino and antineutrino channels. We show that it automatically resolves the problem of parameter ambiguities which involves \delta, \theta_{13}, and the sign of \Delta m^2_{13}.Comment: 15 pages, 3 figures, minor corrections, final version to appear in PL